1. Field of the Invention
This invention relates to the field of substrates used in the manufacture of semiconductor devices and methods used in the processing of such substrates.
2. Brief Description of Related Developments
Telecommunications equipment, and in particular equipment for optical communication networks, have had significant performance increases due to the use of III-V semiconductor materials such as indium, phosphorus, gallium and arsenic. As the performance of devices and systems based upon III-V devices increases, new mechanisms that interfere with the operation of the devices are identified. It is the object of the present invention to reduce the deleterious effect of one such mechanism within indium phosphide (InP) devices.
According to a first aspect of the invention there is provided a semiconductor device comprising a substrate of III-V semiconductor material, an oxide layer permanently formed on a surface of the substrate, the oxide layer having a significant concentration of a dopant material, and a plurality of epitaxial semiconductor layers formed on the oxide layer, wherein the oxide layer prevents diffusion from the substrate into the plurality of epitaxial semiconductor layers.
The III-V semiconductor material may be indium phosphide and it may be doped. The III-V semiconductor material may be doped with an n-type dopant. The dopant material deposited on the oxide layer may be silicon.
The plurality of epitaxial semiconductor layers may comprise a first cladding layer formed upon the substrate, an active region formed upon the first cladding layer, and a second cladding layer formed upon the active region.
According to a second aspect of the invention there is provided a method of manufacturing a semiconductor device, the method comprising the steps of: heating a substrate comprising a layer of a III-V semiconductor material to desorb a first oxide layer previously formed on a surface of the substrate, depositing dopant material on the desorbed surface of the semiconductor substrate, oxidizing the semiconductor substrate to form a further oxide layer comprising a significant concentration of the dopant material, and depositing a plurality of epitaxial layers of semiconductor material on the substrate.
The method may further include step of depositing a first cladding layer on the substrate, depositing an active region on the first cladding layer, and depositing a second cladding layer on the active region.
The method may comprise the additional step of etching one or more of the plurality of epitaxial layers of semiconductor material to form a mesa. Furthermore, the method may include the step of depositing one or more blocking layers of semiconductor material on the sides of the mesa.
The dopant material may be selectively deposited on the surface of the semiconductor substrate. Alternatively, the oxide layer comprising a significant concentration, of dopant material may be selectively etched from the surface of the semiconductor substrate. The dopant material may be silicon and it may be deposited by flowing a gas over the semiconductor substrate. The semiconductor substrate may be oxidized by exposing the semiconductor substrate to an oxidizing agent.
The method may also comprise the steps of depositing dopant material on each side of the mesa, oxidizing each side of the mesa to form oxide layers comprising a significant concentration of dopant material, and depositing one or more blocking layers of semiconductor material on the oxide layers.
The method may comprise the further step of: depositing one or more further epitaxial layers of semiconductor material on the previously deposited plurality of epitaxial layers and the uppermost blocking layer.